Effective Parameters of Terahertz Metamaterials Fabricated with Microfluidic-Jet Technique
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Effective Parameters of Terahertz Metamaterials Fabricated with Microfluidic-Jet Technique Zsolt Szabó, Yew Li Hor, Er Ping Li and Wolfgang J. R. Hoefer Advanced Plasmonics and Photonics Group, A-Star Institute of High Performance Computing, 1 Fusionopolis Way, 16-16 Connexis, 138632, Singapore ABSTRACT A cost-effective fabrication method to engineer metamaterial structures with micrometersize features and novel mechanical properties, which are suitable for terahertz applications, is reported herein. The effective metamaterial parameter extraction procedure is employed with the Kramers-Kronig relation to analyze the effective parameters of single- and multilayer metamaterial structures. INTRODUCTION As frequencies increase towards the optical range, magnetisation vanishes in all natural materials and the refractive index is always positive. However, novel types of artificial composites called metamaterials were proposed with the striking property of having a negative refractive index [1]. The first physical realization of such a metamaterial was presented ten years ago for microwave frequencies [2]. Since then, researchers have increased the operating frequency of metamaterials to higher values, including the terahertz and even optical frequencies. A conventional metamaterial design containing split-ring resonators and microstrip wires to achieve the negative refractive index is considered [3]. The novelty of the proposed fabrication procedure is the application of the microfluidic jet technique, which is a costeffective way to manufacture large areas of metamaterials. This technique allows printing of metallic structures on a large variety of substrates. In particular, by selecting a lightweight or flexible substrate, metamaterials with novel mechanical properties can be manufactured. This can be advantageous, for example in cloaking studies, to cover a cylindrical structure with a metamaterial. To characterize the fabricated metamaterial structures, the effective metamaterial parameters are retrieved from calculated S parameters. In order to ensure the uniqueness of the effective parameters, the procedure employed here applies the Kramers-Kronig relations to estimate the real part of the refractive index from the extinction coefficient [4]. In practical applications, a metamaterial which is only one unit-cell thick, is not very useful. Therefore we present the calculated effective parameters of single-and multi-layer metamaterials and we comment on the obtained results. EXPERIMENTAL DETAILS The microfluidic-jet technique is a cost-effective planar process, which allows mass production of metamaterial structures operating at terahertz frequencies [5]. It is a planar process, yet a three-dimensional metamaterial can be made by stacking several planar metamaterial layers together. In the process presented, liquid polyimide is applied as masking
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